The use of intraluminal stents has had increasing acceptance and use in the treatment of various medical conditions. Intraluminal stents can be used to maintain the patency of blood vessels and other body lumens, such as in the treatment of urological disorders, among others. The use of stents to maintain open a coronary or other artery after an angioplasty procedure has been performed has become a common practice. Over the past decade, various stent designs have been described and used. Many have been of the type in which the stent is in a tubular configuration that can be expanded from a relatively small diameter adapted for delivery through the vasculature (low profile) to a larger deployed diameter by mounting the stent on the balloon of an inflatable balloon catheter and then advancing the catheter to place the balloon mounted stent at the intended site of deployment. The balloon then is inflated to expand the stent into engagement with the body lumen. The stent maintains its expanded shape to support the body lumen. The balloon then is deflated and the delivery catheter is withdrawn, leaving the stent in place to support the body lumen. The configuration of such stents typically may be considered as generally tubular in which the wall of the tube is defined by variously configured wires or a tubular member that has been shaped to provide a plurality of interconnected wire-like struts or wires. Illustrative examples of such stents may be found in U.S. Pat. No. 4,733,665 U.S. Pat. No. 5,104,404 (Wolff), U.S. Pat. No. 5,421,955 (Lau) and in International Publication WO 96/41591 (Borghi), among others.
The design and placement of a stent can present a number of considerations, particularly when the stent is to be used in an environment where it must be advanced through tortuous anatomy, as is not uncommon in coronary angioplasty. The stent must have the ability to maintain its tubular configuration when expanded in the body lumen in order to maintain the body lumen open. It also should have sufficient longitudinal flexibility, when mounted in its low profile on the balloon, so that it can be advanced through curved, sometimes tortuous, blood vessels in order to reach the deployment site. Additionally, the position of the stent on the balloon should be maintained without shifting longitudinally, as the balloon mounted stent is advanced to the deployment site. That can present particular difficulty when the stent and balloon to which it is mounted must be passed through sharply curved tortuous anatomy or anatomy where the lumen has become narrowed or otherwise partly obstructed regions. Should the stent engage a blood vessel in a sharply curved or somewhat narrowed region and consequently, shift longitudinally on the balloon as the catheter is advanced or manipulated, the balloon, when inflated, may not expand the stent fully along the length of the stent. In some cases, the stent could be dislodged from the balloon without the ability to retrieve it.
The importance of maintaining the stent securely on the balloon has been recognized in the prior art. A number of approaches have been proposed. Some simply slide the stent onto the balloon and crimp it tightly about the balloon. That may risk damage to the balloon or the stent and also may result in a relatively longitudinally stiff stent. Other stent retention devices have been proposed including the use of a sleeve to overlie the stent during advancement, with the sleeve being retracted when the stent is to be deployed. Still other approaches have included the use of end caps mounted on the catheter and adapted to temporarily engage the ends of the stent while permitting the stent ends to release when the stent is expanded as is shown in U.S. Pat No. 4,950,227 (Savin). Such devices and techniques generally have required compromises of one or more desirable features of the stent. The desirable low profile or longitudinal flexibility may be compromised as well as the security of retention. It would be desirable to provide a balloon mounted stent and method for such mounting that would reduce the extent of compromise of desirable characteristics of the stent and its delivery system.